I’ve been doing some googling, and it seems that gluing up different species of wood is a bad idea due to differences in wood movement.

However, I saw a post on here a few months ago (can’t find it now!) where a guy made a real impressive bartop by joining Cherry, Maple, and Walnut. Nobody seemed to give him grief about joining the different species.

I’d like to build a coffee table, and am a sucker for the contrast between walnut & maple. What are some precautions I ought to take when gluing these up and preparing for the project?

I can’t imagine why gluing up different woods in a panel could cause a problem. Even if part of it expands and contracts a bit more than its neighbors it’ll only do so across its width, causing the panel as a whole to move. I can see how it might be an issue in a butcherblock-style glue-up. If you made a solid box out of very different species it could pull apart the dovetails or boxjoint at the corner. But (unless I’m missing something) it wouldn’t be a concern at all in a panel glueup with long-grain to long-grain joints.